Copper indium diselenide (CuInSe2, or CIS) and its higher band gap variants, such as copper indium gallium diselenide (Cu(In,Ga)Se2, or CIGS), and any of these compounds with sulfur replacing some of the selenium represent a group of materials, referred to as copper indium selenide CIS based alloys, have desirable properties for use as the absorber layer in thin-film solar cells as used in photovoltaic modules. These layers are susceptible to damage from water and/or water vapor.
Photovoltaic (“PV”) modules used in residential structures and roofing materials for generating electricity often require additional protection from environmental damage, such as an ingress of water, that can reduce an active lifetime of the photovoltaic system. Additionally, these modules require protection from hail, rocks, or other objects that may impact their surfaces.
Rigid or flexible sheets of glass may be used to support and/or provide protection to the underlying semiconductor layers. These sheets, however, may themselves be susceptible to cracking when impacted, thereby exposing the semiconductor layers to moisture and other environmental conditions that diminish the lifetime of the cell or completely destroy it. Also, certain impacts may cause cracks that do not extend to the underlying semiconductor layers initially, but may propagate over time, for example during thermal expansion and contraction cycles resulting from change of temperature during the day, or over several months and seasons.
Additionally, flexible glasses are susceptible to weakness from micro scratches produced during processing, and/or abrasion during weathering. These microscratches and abrasions act as stress concentrators and/or crack initiation sites which may compromise resistance to impact and/or resistance to moisture barrier properties.
Furthermore, plural impacts over a narrow radius can exceed the tensile strength of the glass and cause breakage.